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COMPOSITION OF GREEN MANURES 
AT DIFFERENT STAGES OF GROWTH 



A THESIS 

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 
OF CORNELL UNIVERSITY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 



BY 



THOMAS LYSON5 MARTIN 



JUNE, 1919 



Reprinted from Bulletin 406, August. 1 921. of Cornell University Agricultural 
Experiment Station. 



DECOMPOSITION OF GREEN MANURES 
AT DIFFERENT STAGES OF GROWTH 



A THESIS 

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 
OF CORNELL UNIVERSITY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 



BY 



THOMAS LYSONS MARTIN 

JUNE, 1919 



Reprinted from Bulletin 406, August. 1921, of Cornell University Aj>rlcultural 
Experiment Station. 






-b 






r 



CONTENTS 

^c) PAGE 

Review of literature 139 

Experimental work 141 

Plan of the investigation 141 

Results 145 

Effect of stage of growth of green manure on rate of htmius 

formation i45 

Effect of stage of growth of green manure on rate of 

nitrification in soil 147 

Effect of stage of growth of green manure on increased 
availability of nutrients as measured by effect on 

subsequent plant growth . 151 

Consideration of experimental error 154 

Summary 155 

Conclusion 156 

Literature cited 157 

Appendix 159 



137 



DECOMPOSITION OF GREEN MANURES AT DIFFERENT 
STAGES OF GROWTH 

Thomas Lysons Martin 

The value of organic matter in soil improvement has long been recog- 
nized. It benefits the tilth of the soil, affects the availability of the 
nutrients, stimulates bacterial activity, and gives to the soil a greater 
crop-producing power. Farm manures and green manures are the principal 
sources of this organic material. Green manures, as one of the sources 
of organic matter, are increasing in importance as the need for soil humus 
is becoming more widely recognized. 

The humus stage of decomposition is in all likelihood the period at 
which many of the desirable effects of manures are produced. The ease 
with which a manure reaches this stage is probably a measure of its 
effectiveness. It is well known that plants vary, according to their 
degree of maturity, in the readiness with which they are broken down 
into humus. However, the exact stage of growth at which the crops 
used as green manures decompose most rapidly and exert their greatest 
influence on the soils so treated is yet to be determined. 

The investigation here described was undertaken with the purpose of 
throwing some light on this question. 

REVIEW OF LITERATURE 

A survey of the literature of the subject indicates that the work thus 
far has been only of a general nature. The effect of the manures on the 
soil has been studied, and incidentally, in these studies, it has been found 
that the young material, as compared with the old, decomposes more 
rapidly. Not much attention has been given to attempting to find the 
period when the plant used as a green manure decomposes most rapidly 
and has the greatest influence on the various soil activities. 

Muntz (1890)^ in his investigations, found that the value of green 
manuring is proportional to the rapidity with which the nitrogen is 
converted into nitrates. 

Snyder (1895) placed a mixture of soil and green clover in boxes and 
allowed it to ferment for one year. In a majority of cases he found an 
increase in the availability of the phosphorus and the potassium of the 
soils so treated. 



'Dates in parenthesis refer to Literature Cited, page IS7. 

Author's acknowledgment. The writer acknowledges the help received from Dr. J. A. Bizzell, under 
whose direction this work was done. 



I40 Bulletin 406 

Conn (1901) says: 

The building of nitrates will not take place in the soil so long as there is any consider" 
able amount of organic material or any considerable amount of free ammonia present- 
If there is much organic material rapidly decomposing so as to produce ammonia, this 
will completely check the formation of nitrates, for these nitrifying bacteria will not 
grow in the presence of either organic material or ammonia. It is not until after 
decomposition has been completed and practically all the organic compounds used up 
that the nitrifying germs can begin to act. 

Marshall (191 2) states that under suitable conditions the accumulation 
of humus in the soil stimulates nitrification to a very striking extent. 

Velbel (19 1 4) found that soil nitrification increases directly with the 
rate of decay of the humus-forming material. 

Hutchinson and Milligan (19 14) used nitrate acctunulation in the soil 
as a measure of organic decay and found that the percentage of nitrification 
decreased markedly with the age of the green material added. 

Hill (191 5) found that the nitrogen of green manures appears to pass 
rapidly into the nitrate form as the decay processes advance. 

Using chemical analyses and subsequent crop growth as a measure, 
Hopkins and Aumer (19 15) found that decomposing green manures in- 
crease the availability of the nutrients in the soil. Potassiimi seemed 
particularly influenced. 

Wright (191 5) plowed under green manure, which decayed rapidly, 
the decay being accompanied by vigorous nitrification. When resistant 
material was added, it reduced the rate of nitrification. 

Brown and Allison (19 16) claim that the application of large quantities 
of humus-forming material to soils increases ammonification and nitrifica- 
tion to a very considerable extent. They found that straw, due to its greater 
resistance, does not increase nitrification as much as do green manures. 

White (19 1 6), utilizing crimson clover as a green manure, found that 
the yoimger the crop when plowed under, the more rapidly did it decay. 
A corresponding stimulation was also observed in the growth of a 
subsequent tomato crop. 

Maynard (191 7) studied the rate of decomposition of a sweet-clover 
green manure, and, using the accumtdation of nitrates in the soil as a 
measure, found that the rate of decay decreases as the maturity of the 
plant tissue is approached. 

Carr (19 17) suggested that, since humus formation is a step in the 
process of decomposition, the rate of decay may be measured by the 
rate at which humus is produced. 

Merkle (19 18) used the rate of humus formation and the evolution 
of carbon dioxide as a measure of the degree of decay, and found that 
the greater the succulency of the material studied and the greater its 
nitrogen content, the more rapidly does it decay. 



Decomposition of Green Manures 141 

These citations suffice to show that green manures are of value; that 
the younger the material when incorporated with the soil, the more rapidly 
does it decompose; and that as it decomposes, its favorable influence on 
the soil is proportional to the rate of decay. This information is all of 
a general character. There is nothing to indicate the exact stage in the 
growth of the plant at which these favorable influences occur. The 
knowledge that has been obtained has been based on a single method of 
measurement of the rate of decay. Unfortunately, no one method has 
been devised which in every respect satisfactorily indicates the rate of 
organic decomposition in soils. It therefore becomes necessary, in investi- 
gations of this nature, to use a variety of methods, each one of which will 
tend to check up the others. The results from such a procedure should 
consequently be more conclusive than results otherwise obtained. 

It is the aim of the present investigation to follow such a plan, and to 
determine, if possible, at what stage of growth the crops used as green 
manures decompose most rapidly and what effect this stage has on the 
soil so treated. 

EXPERIMENTAL WORK 

PLAN OF THE INVESTIGATION 

The method of conducting the investigation here discussed is briefly 
outlined as follows: 

Dunkirk clayey silt loam, a glacial-lake soil comprising the larger part 
of the soil on the Cornell University experimental farm, was used in the 
work. This soil was passed thru a 2-millimeter sieve, and samples of 3600 
grams each were then weighed into one-gallon jars, the inside dimen- 
sions of which were 7I by 7 inches. 

Rye, oats, and buckwheat were used as green manure, each crop being 
obtained at three different stages of growth. The material, while still 
fresh, was cut into pieces of about one inch in length, and thoroly mixed 
with the soil. The mixture was then brought to and maintained at a 
moisture content of 25 per cent, and was kept at a constant temperature 
in the greenhouse. Untreated soils served as checks. All incorporations 
were made in triplicate. 

The investigation consisted of a series of three experiments and covered 
a period of three years. The experimental series were as follows: 

Series 19 16. Equal green weights of rye, oats, and buckwheat, respec- 
tively, at three stages of maturity, were incorporated with separate samples 
of soil and incubated for twelve months. 

Series 191 7. Equal dry weights of the same crops were added to 
separate soil samples and incubated for four months. 



142 



Bulletin 406 



Series 191 8. Nine areas of soil were sown to rye, oats, and buckwheat, 
respectively, three areas being given to each crop. Green material, 
representing the first, second, and third stages of maturity for each crop, 
was then successively obtained from the respective areas, for incorporation 
with the soil to be experimented on. With increase in maturity, there 
was, of course, a corresponding increase in the green and the dry weights 
added to the soil, thus approximating field conditions. 

The areas selected for the rye crop were each 4.4 square feet, the total 
material produced at each stage being divided equally among the three 
triplicate pots. The areas for oats and buckwheat were 4.5 and 3.4 
square feet, respectively. These crops were treated exactly as was the^ 
rye. 

In representing the successive stages of maturity in the tables and 
diagrams on the following pages, the letters A, B, and C are used. For 
the three series, and for the three different crops used, the stages of growth 
indicated by these letters are as follows : 

Series 1916 



Crop 


Height 


Condition 


fA 
Rye B 

[c 


16 inches. . . 
38 inches. . . 
60 inches . . . 


Boot stage 
Well headed 
Almost ripe 


fA 

Oats B 

C 


10 inches. . . 
24 inches . . . 
36 inches . . . 


Preceding boot stage 
Boot stage 
Almost ripe 


f A 

Buckwheat \ B 

C 


12 inches. . . 
30 inches . . . 
36 inches. . . 


Blossoming 
Well blossomed 
Seeds forming 


Series 1917 


Crop 


Height 


Condition 


A 
Rye B 


60 inches . . . 
65 inches. . . 
72 inches. . . 


Fully headed 
Heads yellow 
Ripe 


'A 

Oats B 

,C 


48 inches. . . 
60 inches . . . 
62 inches. . . 


Fully headed 
Heads yellow 
Ripe 


Buckwheat -^ B 

IC 


40 inches . . . 
48 inches. . . 
48 inches. . . 


Well blossomed 
Seeds forming 
Ripe 



Decomposition of Green Manures 
Series 1918 



143 



Crop 


Height 


Condition 


Rye B 

[c 


24 inches . . . 
48 inches. . . 
48 inches. . . 


Preceding boot stage 
Blossoming 
Almost ripe 


(A 

Oats -^ B 

,C 


1 1 inches . . . 
30 inches . . . 
36 inches . . . 


Boot stage 
Well headed 
Almost ripe 


(A 

Buckwheat -^ B 

,C 


10 inches. . . 
20 inches . . . 
26 inches. . . 


Blossoming 
Well blossomed 
Almost ripe 



After various periods of incubation, soil samples were taken from each 
of the pots and analyses were made to determine the rate of decay. 

With investigations of this nature, the methods used for determining 
the amount of decomposition are of prime importance. As previously 
stated, no single method has been devised which in every respect satis- 
factorily indicates the rate of organic decay in soils. The methods already 
suggested, and tested to some extent, are as follows: (i) determination 
of the rate of humus formation; (2) determination of the rate of evolution 
of carbon dioxide; (3) study of the accumulation of nitrates; and (4) study 
of the increased availability of plant nutrients as measured by the effect 
on subsequent plant growth. 

Each of these methods is open to objection. In making humus deter- 
minations, the humus extract is difficult to filter and the process is in 
consequence associated with such a large experimental error that the 
results are not dependable. Gortnsr (191 7) used this method and found 
no evidence that an increase in soil humus was brought about by specific 
humification. He found maximum ammonia-soluble material present in 
the soil immediately after green manures were turned under and before 
humifying bacteria could have begun work. Carr (191 7) obtained similar 
results while attempting to discover whether the humus content of the 
soil was a measure of its fertility. Christie (19 16), studying the decom- 
position of organic matter in the soil, stated that the percentage of humus 
was not necessarily an index of the value of the organic matter in the soil. 

The rate of evolution of carbon dioxide as an indicator of the rate of 
decay is dependent on a number of soil conditions. The looseness which 
the organic material produces in the soil influences the ease with which 
the carbon dioxide is extracted. The amount of carbon dioxide utilized 
by the bacteria as a source of carbon is also a factor. Moreover, certain 
groups of organisms in the soil produce only intermediate products, such 



144 Bulletin 406 

as butyric and acetic acids, and this condition must also be considered 
in using this method. 

When the accumulation of nitrates is used as a measure of organic 
decay, the possibility of a large probable error should not be overlooked; 
for much of the nitrogen that might otherwise be changed to nitrates is 
used by the organisms present in the soil, while the method used for 
obtaining a soil extract for nitrate determination may introduce a further 
source of error. 

The increased crop growth on soils receiving treatments of decaying 
organic materials may be due to factors other than the increased availability 
of plant nutrients. The tilth is improved by the placing of the soil in 
the pots; and this, in turn, has a stimulating effect on the biological and 
chemical reactions in the soil. 

The foregoing criticisms of the means available for measuring the rate 
of organic decay indicate that the use of one method alone may not give 
very dependable results. As previously stated, it is obviously better, in 
an investigation of this kind, to use several methods, each one tending 
to check up the others. The results obtained from such a procedure 
should be more conclusive by far. 

In the present investigation, the following methods were used to 
measure the rate of decay: 

(i) Determination of the rate of humus formation; 

(2) Study of the accumulation of nitrates; 

(3) Study of the increased availability of plant nutrients as measured 
by the effect on subsequent plant growth. 

The method of measuring the rate of decay by a determination of the 
rate of evolution of carbon dioxide was omitted because it was thought 
that three methods, each one of which would tend to check up the others, 
would give amply significant results. 

The amount of humus in the soil sample obtained from each pot was 
determined according to the method recommended by the United States 
Bureau of Chemistry (191 2), with the exception that 50 grams of soil 
was used instead of 5 grams. The humus extract was filtered thru a 
lo-centimeter Buchner funnel, the treated soil serving as a filter. 

Nitrates were determined according to the method given by Schreiner 
and Failyer (1906). 

Total nitrogen was determined according to the Kjeldahl-Gunning 
method (U. S. Bureau of Chemistry, 19 12). 

After the soils had been sampled for analysis, wheat was planted in 
each pot and grown to maturity. The moisture content, while the crop 
was growing, was kept at 25 per cent, the optimum condition for this 
particular soil. 



Decomposition of Green Manures 145 



Effect of stage of growth of green manure on rate of humus formation 
It would appear in general, from the curves shown in figures 28 and 29 
that the greater the succulency of the manure when incorporated with 
the soil, the larger is the amount of humus formed. 

The first marked exception to this generalization, however, appears in 
figure 27, showing the results of allowing the material to decompose for 
twelve months. Here, in every instance, the most succulent crop resulted 
in the least amount of humus. This is in exact opposition to the results 
shown in figures 28 and 29, when the manure was allowed to decompose 




Fig. 26. ST.\GES of incre.a.se .\nd decrease in humus production 

The A-B part of the figure represents the period of humus formation, during which humus is formed 
and no end products are developed. B-C indicates the stage in which there is a humic-decomposition 
process at work and end products are formed as rapidly as the humus is produced from the crude organic 
material. C-D represents the stage in which the humic-decomposition process is in the ascendancy and 
more end products are produced than there is humus formed. 

for four and five months, respectively. The data given in table I^ from 
which the curves in figure 2 7 were obtained, show that more dry matter 
was added to each soil as the maturity of the manure increased; but the 
rate of increase of this dry matter added was, in general, less than the 
rate of increase of the humus formed. 

It would seem that in the breaking down of the crude organic material 
of the soil into its end products, there occur a period of humus formation 
and a period of himius decomposition, involving three distinct steps which 
are illustrated in figure- 26. 

With this understanding of the process, the results shown in figure 27 
may be explained. In all probabiHty the earliest stages of maturity, the 

*A11 tables are found in the appendix pages 159-169. 



146 



Bulletin 406 



A stage, of the rye, oats, and buckwheat, in the 19 16 series, had reached 
that phase of organic decay indicated by C-D in figure 26. The older 
materials, the B and C stages of the same crops, were still in the stage 
during which the production of humus and the development of the end 
products balance each other. 

Where the period of incubation was shorter, as shown in figures 28 and 
29, the most succulent material used as manure was probably well along 



35 



30 
A 

25 

■p 
o 
a 

I20 

v 
3 

3 15 

"o 
w 

e 

O 10 



y 




y^ 

/ 




/ 






^ • * " 
- - - 




-••..• Oofs 











B 



-Maturity of green manure- 



FiG. 27. 



SERIES I916. EFFECT OF MATURITY OF GREEN MANURE ON AMOUNT OF HUMUS 
FORMED AT THE END OF TWELVE MONTHS 



The weights of green material were constant 
(Data given in table i) 



in the period represented by the B-C part of figure 26, while the materials 
added at their maturer stages were still in the period of himius formation. 
In figure 28, the curve for buckwheat is a second exception to the original 
generalization — that the greater the succulency of the manure when 
incorporated with the soil, the larger is the amount of humus formed. 
This may be accounted for by the probability that the youngest and most 
succulent material incorporated had decomposed very rapidly and was 
in the period of htmiic decomposition at the time of the analysis. 



Decomposition of Green Manures 



147 



It appears, from this study of the rate of humus formation, that the 
decomposition of the green-manure crop, when incorporated with the 
soil, is most rapid when the crop is at the half- mature stage, the early- 
blossoming period. This applies to all the crops studied. 



90- 



80- 



70- 



"S 60- 



B50- 

a 

a 
b 

•d 

"o 40- 



30- 



20- 



OC7fS 



10' 



0- — »- 



B 



-Maturity of green manure- 



FlG. 28. SERIES 191 7. EFFECT OF MATURITY OF GREEN MANURE ON PERCENTAGE OF 
DRY MATTER HUMIFIED AT THE END OF FOUR MONTHS 

The weights of dry matter were constant- 
(Data given in table 4) 

Effect of stage of growth of green manure on rate of nitrification in soil 
As already stated, the accumulation of nitrates was also used as a 

measure of organic decay. The results of this method, as expressed in 

figures 30, 31, and 32, show that the process of nitrification goes on most 

vigorously with the most succulent material. 

In figure 31, evidence of nitrification is lacking for rye and oats in the 

two later stages of maturity. It is unjustifiable to conclude, however, 



148 Bulletin 406 

that no nitrification has occurred, for evidence is given in table 2 and in 
the curves for humus (figures 27, 28, and 29) that some decomposition has 
taken place. It is probable that these two exceptions are due to the 
fact that nitrification has not become siifficiently pronounced to respond 
to the tests. Moreover, the nitrogen rendered available has perhaps 
been converted into some other form by the organisms of decomposition. 
This idea is supported by Gainey (19 14), who shows that in using the 




-Maturity of green manure- 



Fig. 29. SERIES 191 8, effect of maturity of green manure on percentage of 

DRY matter humified AT THE END OF FIVE MONTHS 

The green material at each stage came from equal soil areas, but were, of caarss, different in amounts 
(Data given in table 7) 

acciunulation of nitrates as a measure of the nitrifying power, one is 
confronted with the difficulty that the nitrates are sometimes used as a 
source of nitrogen by the saprophytic organisms of the soil. 

In the curve for buclcwheat in figure 30, the youngest material shows the 
least amount of nitrification as compared with the later stages of -growth. 
In figure 31, the most succulent period, compared with the medium or 
jB-stage, of maturity, indicates the same result. A physical examination 
of the soil itself, at the time of sampling for analysis, revealed that the 



Decomposition of Green Manures 



149 




-Maturity of green manure- 



FlG. 30. SERIES I916. EFFECT OF MATURITY OF GREEN MANURE ON AMOUNT OF 
NITRATES FORMED AT THE END OF TWELVE MONTHS 

The weights of green material added to the soil were constant 
(Data given in table 2) 




Fig. 31. SERIES 19.17. effect of maturity of green MANURE ON NITRIFICATION 
PROCESS AT THE END OF FOUR MONTHS 

The weights of dry matter added were constant 
(Data given in table 5) 



15° 



Bulletin 406 



older material used for incorporation had not been fully broken down 
during the period of incubation. The soil containing the most succulent 
manure gave no physical evidence that organic matter was present, 
complete decomposition having apparently occurred. 

The question arises as to what has happened to the nitrates in this 
stage of complete decay. As mentioned previously, Gainey (19 14) has 
shown that the nitrates are used as a source of nitrogen by the saprophytic 
organisms in the soil. Doryland ( 1 9 1 6) presents data showing the reduction 



35- 



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30- 



. Oc/^s 



5 25- 



Biytckiyheat 



20. 



15. 



fe 10- 



B 



-Maturity of green manure- 



FiG. 32. 



SERIES 191 8. EFFECT OF MATURITY OF GREEN MANURE ON NITRIFICATION 
PROCESS AT THE END OF FIVE MONTHS 



The green manure at each stage came from equal soil areas 
(Data given in table 8) 

of nitrates in the soil to other forms of nitrogen, whereby no loss of nitrogen 
has occurred, as revealed by the analysis of the total nitrogen content 
of the soil. It is probable that the nitrates are utilized by the organisms 
present. In fact, the writer has found that the total number of organisms 
was much greater in the soil receiving the succulent buclcwheat than in 
that to which material of a later stage of maturity had been added. 

Conn (1901) claims that in the process of decay, nitrification does not 
occur until toward ^he end of the decomposition period. There is evi- 



Decomposition of Green Manures 151 

dently too great an accumulation of carbon dioxide at first to allow the 
nitrifying organisms to work. Nevertheless it is not probable that the 
nitrifying process is entirely eliminated. Altho it is possible for some 
nitrates to be produced continuously, they are probably utilized as fast 
as they are formed. Later, when the decomposition process slows up, the 
oxygen replaces the carbon dioxide and a favorable environment prevails 
for the nitrifying activities. It would appear, from this, that conditions 
particularly favoring the accumulation of nitrates are present at the later 
stages of decomposition. This supports the conclusion that plant tissue 
at the period of greatest succulency — the half-mature stage of green 
material — decomposes so readily when incorporated with the soil, that 
its nitrogen very quickly becomes available to the organisms that control 
nitrate formation. 

Effect of stage of growth of green manure on increased availability of nutrients 
as measured by effect on subsequent plant growth 

When crops were grown on soils previously treated with green manures 
of varying degrees of maturity, there was a marked stimulating effect. 
This was greatest with the most succulent additions, and was probably 
due to an increased availability of soil nutrients. The data on these 
results are shown diagrammatically in figures 33, 34, and 35. 

The amount of dry matter added in the 19 16 and 1918 series varied 
with the maturity of the manure used, the pots treated with the maturer 
material receiving the larger amounts of dry matter. In the 191 7 series 
the dry matter was kept constant. This was done in order to learn 
whether the effects produced by increased maturity were due to increasing 
the amount of the dry matter, rather than to its lack of succulency. The 
effect seems to be the same in all cases. The crops produced for each 
unit of added dry matter decreased with the increased maturity of the 
additions. The younger the material when incorporated with the soil, 
the greater was the increase in crop growth. 

Why does green manure of maximum succulency at the time of its 
incorporation with the soil produce the most beneficial effect on the 
growth of subsequent crops? It may be because of a more favorable 
effect on the physical condition of the soil. The manure in the succulent 
state imdoubtedly decomposes very readily, and nutrients combined with 
the organic compounds of the tissues are very soon released, thus becoming 
available to the crop. The decomposition products may also react on 
the soil constituents and render them more readily available to the growing 
plants. Decomposition of organic matter in the soil appears to render 
available the essential nutrients in the soil. Jensen (191 7) found increased 



152 



Bulletin 406 



solubility of iron, calcium, magnesium, and phosphorus after alfalfa had 
been incorporated with the soil and allowed to decompose for six months. 
He found also that sweet clover, after decomposing for three months in 
the soil, increased the solubility of the phosphorus present from 30 to 
100 per cent; and he states further that the amounts of available calcium, 
magnesium, iron, and phosphorus in citrus soils are measurably increased 
by the addition of decaying organic material. Hopkins and Aumer (1915) 
claim that the nitrite organisms associated with the decaying processes 



35 



30 



25 



20 



■^ 13 



10 







>N^^ 




x^^ 


(?<7/y 


% ^^ 


^ 


X 

X 


^'^V^ 


X 

X 


^ « ^^^^. 











A B < 

< Maturity of green manure > 

Fig. 33. SERIES 1916. effect on growth of a subsequent wheat crop produced 

BY the incorporation IN THE SOIL OF GREEN MANURE AT VARIOUS STAGES OF 
MATURITY AND THE SUBJECTION OF THE MIXTURE TO A TWELVE-MONTHS INCUBATION 
PERIOD 

The weights of green material added were constant 
(Data given in table 3) 



render available the insoluble phosphorus in the soil. Hopkins and 
Whiting (19 16) applied green manures to soil residues from which the 
soluble potassium had been extracted. Sufficient insoluble potassium 
was liberated thereby to enable clover to grow luxurianth'- when treated 
with lime and phosphorus. Snyder (1897) treated soils with green 
manures, and after allowing fermentation to proceed for one year he found 



Decomposition of Green Manures 



153 



a considerable increase in the amount of available phosphorus and 
potassium in the soil himius. He attributes these results to the large 
amounts of carbon dioxide given off by the decaying organic matter, 
since this gas acts as a solvent on the minerals of the soil. Truog (19 12) 
shows in his work that the availability of the insoluble compounds of 
phosphorus is due to the carbon-dioxide accumulations brought about by 
the decay of green manures. 



36 



30- 



25 



.S 20 



£ 13. 



Ffc/e 



Oafs 



— "^Buc/fH/heat 




B 



< ' Maturity of green manure > 

Fig. 34. SERIES 1917. effect on growth of a subsequent wheat crop produced 

BY THE incorporation IN THE SOIL OF GREEN MANURE AT VARIOUS STAGES OF 
MATURITY AND THE SUBJECTION OF THE MIXTURE TO A FOUR-MONTHS INCUBATION 
PERIOD 

The weights of dry matter added were constant 
{Data given in table 6) 



It would appear, therefore, that decaying organic matter renders 
available the otherwise insoluble plant nutrients in the soil. The 
decomposition products, such as carbon dioxide and butyric, acetic, 
lactic, and other organic acids, are in all probability the causative factors 
for much of this increase. The more rapid or more complete the decay 
process, the more quickly do the decomposition products accumulate, 
accompanied by an increased amount of available nutrients. As an 



154 



Bulletin 406 



increase in the availability of the plant nutrients in soil may be measured 
by the growth of crops, it is reasonable to conclude, from the foregoing 
data, that the increased crop yields from the soils receiving the more 
succulent manure were due to an increase in the availability of the nutrients 
in the soil. 

CONSIDERATION OF EXPERIMENTAL ERROR 

In order to determine the degree of significance of the data just presented, 
and also to obtain a check on the accuracy with which the various analyses 



33- 



30" 



25' 



C 20- 



13- 



10- 



ffi^e 



Oafs 

'Buckty/7eat 




0_. 



B 



< — • • — Maturity of green manure • — > 

Fig. 35. SERIES 191 8. effect on growth of a subsequent wheat crop produced 

BY THE incorporation IN THE SOIL OF GREEN MANURE AT VARIOUS STAGES OF 
maturity and THE SUBJECTION OF THE MIXTURE TO A FIVE-MONTHS INCUBATION 
PERIOD 

The green manure at each stage came from equal soil areas 
(Data given in table 9) 



were performed, it was considered necessary to calculate the experimental 
error for the data obtained. This was done by finding the arithmetical 
mean values of the dry matter humified, of the nitrogen nitrified in the 
green manure, and of the total crop grown on the soils variously treated. 
The first two sets of means were expressed in percentages, the third in 
grams of dry matter produc-ed. The probable error of these mean values 



Decomposition of Green Manures 155 

was then determined according to Peter's formula, as given by Mellor 
(1909). The formula is as follows: 

R = ± o.84534f^ 
n\n-i 

R represents the probable error ; 2" ( + v) indicates the sum of the devia- 
tions of every observation from the mean, the sign of each deviation being 
disregarded.; n denotes the number of observations actually made. 

Before conclusions could be drawn as to the rate of decomposition of 
the green-manure crops, the following question was of necessity considered : 
Are the differences in the percentages of dry matter htimified, in the grams 
of crop grown, and in the percentages of nitrogen nitrified in the green 
manure, in the variously treated pots, large enough to be significant? 
This question could be answered only by determining these differences 
and then calculating the probable error of each. The probable error was 
obtained by the use of the following formula : 

E=-\( Ei^-j-Eg^ 
In this formula Ei and E2 represent the probable errors of the values to 
be compared. Wood and Stratton (19 10) state that such differences, to 
be significant, must be greater than 3.8 times the probable error. This 
would mean that the chances are thirty to one that such differences are 
due to treatment. 

It is evident that the differences existing between the results obtained 
from pots treated with the most succulent manure and those from pots 
treated with manure at more advanced stages, are evidently greater 
than 3 .8 times the probable error. Hence they are significant. In general, 
the differences existing between the two maturer stages, B and C, are 
not large. This is true not only for the hinnus data, but also for the 
nitrate and crop figures as well. It indicates that as the crops used for 
green manures approach maturity, the results show proportionately less 
benefit derived. 

SUMMARY 

The value of organic matter in soil is dependent on the ease with which 
it decays. The more rapidly it decomposes, the more quickly can it be 
used by the various agencies within the soil. 

The greater the succulency of the crops used as green manures, the 
more quickly do they decay. 

When crops are about half grown, they are at the point of maximiun 
succulency. This is also the stage at which enough bulk has developed 
to create a fairly large increase in organic matter when the crop is 
incorporated with the soil. 



156 Bulletin 406 

Soils receiving incorporations of green manures at the half-mature 
stage, A, produced the largest crop yields when subsequently cropped. 

Increasing amounts of dry matter added to a soil, in conjunction with 
increased maturity, have the same general effect on the humus formation, 
the accumulation of nitrates, and the crop growth, as does the addition 
of equal weights at each stage of increased maturity. 

The more rapid the decomposition of green manures, the greater is the 
increase in the availability of plant nutrients in the soil, as shown by 
greater crop yields. 

The younger the organic matter used, the larger is the percentage of 
total nitrogen present therein. -^ 

Nitrates accumulate at the greatest rate when green manures of 
maximum succulency are incorporated with the soil. ' 

Some of the nitrates formed in the soil by the influence of green manure 
are probably utilized by growing organisms. 

Nitrates do not accumulate in the soil until the green manures have 
become considerably decomposed. 

The more readily the organic material is decomposed, the more rapidly 
does humus acciunulate and the sooner does it break down to simple 
products. 

The longer the period during which green manures are allowed to humify 
in the soil, the less is the amount of humus found in the soil on analysis. 

There are apparently three periods in the humification of organic matter. 
In the first period humus alone is formed, thus allowing an accumulation 
in the soil. During the second stage humic decomposition sets in and 
the humus is reduced as rapidly as it is formed; accordingly no further 
accumulation is accomplished. In the third period, humus formation 
ceases and the only process at work is that of humus decomposition, 
resulting in a rapid decrease in the amount of humus in the soil. 

Under the same conditions, rye and oats decay at approximately the 
same rate. Buckwheat, however, particularly in the maturer stages, 
decays much more readily than do rye and oats of corresponding maturity. 

CONCLUSION 

In these investigations, using as measurements the rapidity of humus 
formation, the accumulation of nitrates, and the increased availability 
of the plant nutrients, the subsequent crop growth proved that the greatest 
rapidity of decomposition and the greatest benefit to the soil were achieved 
by the use of green manures at the half-grown stage. This is true for 
all three of the green manures used in this series of experiments. 



I 



Decomposition of Green Manures 157 

LITERATURE CITED 

Brown, P. E., and Allison, F. E. Influence of humus forming materials 
of different nitrogen-carbon ratios on bacterial activities. Iowa Agr. 
Exp. Sta. Research bul. 36: 1-30. 1916. 

Carr, R. H. Is the humus content of the soil a guide to fertility? Soil 
sci. 3:515-524. 1917. 

Christie, A. W. The decomposition of the organic matter of kelp in 
the soil. Joum. indus. and engin. chem. 8:425-427. 1916. 

Conn, Herbert W. Agricultural bacteriology, p. 1-357. (Reference 
on p. 103.) 1901. 

DoRYLAND, C. J. T. The influences of energy material upon the relation 
of soil microorganisms to soluble plant food. North Dakota Agr. 
Exp. Sta. Bul. 116:318-401. 1916. 

Gainey, p. L. Real and apparent nitrifying powers. Science n. s. 
39:35-37- 1914- 

Gortner, Ross A. The organic matter of the soil. Soil sci. 3:1-8. 
1917. 

Hill, Harry H. The effect of green manuring on soil nitrates under 
greenhouse conditions. Virginia Agr. Exp. Sta. Tech. bul. 6:119- 
153- 1915- 

Hopkins, Cyril G., and Aumer, J. P. Potassium from the soil. Univ. 
Illinois Agr. Exp. Sta. Bul. 182 : i-io. 1915. 

Hopkins, Cyril G., and Whiting, Albert L. Soil bacteria and phos- 
phates. Univ. Illinois Agr. Exp. Sta. Bul. 190:393-406. 1916. 

Hutchinson, C. M., and Milligan, S. Green manuring experiment, 
1912-13. India Agr. Res. Inst., Pusa. Bul. 40:1-31. 1914. 

Jensen, Charles A. Effect of decomposing organic matter on the 
solubility of certain inorganic constituents of the soil. Joum. agr. res. 
9:253-268. 1917. 

LiPMAN, Jacob G. Bacteria in relation to country life, p. 1-486. 
(Reference on p. 329.) 1912. 

Marshall, Charles E. Microbiology, p. 1-900. (Reference on p. 332.) 
1912. 

Maynard, L. a. The decomposition of sweet clover (Melilotus alba 
Desr.) as a green manure under greenhouse conditions. Cornell Univ. 
Agr. Exp. Sta. Bul. 394: 117-149. 1917. 



158 Bulletin 406 

Mellor, Joseph W. Higher mathematics for students of chemistry and 
physics, p. 1-641. (References on p. 524.) 1909. 

Merkle, Fred G. The decomposition of organic matter in soils. Amer. 
Soc. Agron. Joum. 10:281-302. 1918. 

MuNTz, A. Du role des engrais verts comme fumure azotee. Acad. Sci. 
[Paris]. Compt. rend. 110:972-975. 1890. 

ScHREiNER, Oswald, and Failyer, George H. Colorimetric, turbidity, 
and titration methods used in soil investigations. U. S. Bur. Soils, 
Bui. 31:1-60. (Reference on p. 26-27.) 1906. 

Snyder, Harry. Humus as a factor of soil fertility. In Soi-ls. Univ. 
Minnesota Agr. Exp. Sta. Bui. 41 : 12-31. 1895. 

Production of htmius from manures. In Univ. Minnesota 



Agr. Exp. Sta. Bui. 53: 12-33. i897- 

Truog, E. Factors influencing the availability of rock phosphate. Univ. 
Wisconsin. Agr. Exp. Sta. Research bul. 20:17-51. 1912. 

U. S. Bureau of Chemistry. Official and provisional methods of 
analysis, Association of Official Agricultural Chemists. U. S. Bur. 
Chem. Bul. 107:1-272. (References on p. 7, 19.) 1912. 

Velbel, B. The course of nitrification in fallow soil. Abstracted in 
Exp. sta. rec. 31 : 722. 1914. 

White, T. H. Tests of the use of crimson clover as a green manure for 
tomatoes. In Comparison of commercial fertilizers and stable manure, 
p. 100-106. Maryland State Exp. Sta. Bul. 199:93-106. 1916. 

Wood, T. B., and Stratton, F. J. M. The interpretation of experimental 
results. Joum. agr. sci. 3:417-440. 19 10. 

Wright, R. Claude. The influence of certain organic materials upon 
the transformation of soil nitrogen. Amer. Soc. Agron. Journ. 7: 
193-208. 1915. 



Decomposition of Green Manures 



159 



APPENDIX 



TABLE I. Series 1916.* Effect of Maturity of Green Manure on Amount 
OF Humus Formed at the End of Twelve Months 





Num- 
ber of 
pot 


Green 

manure 
(grams) 


Dry 

matter 
added 
(grams) 


Propor- 
tionate 

amounts 
of dry 
matter 
added 

(per cent) 


Humus formed in 1 2 
months 


Crop 


Total 
(grams) 


Average 
(grams) 


Rye A 


I 

2 
3 


181. 5 


30.9 


100 


14.56 
16.25 
IS. 84 


15.55 ± 0.39 


Rye B 


I 
2 

3 


181, s 


40.0 


129 


22.55 

19.44 
20.60 


20.86 ±0.67 


Rye C 


I 
2 
3 


181. s 


53 


171. 5 


25.10 

21.80 

21 .40 


22.77 ±0.93 


Oats A 


I 
2 
3 


181. s 


38.6 


100 


18.77 
19.64 
14-36 


17.59 ± 1.28 


Oats B 


I 
2 
3 


181. 5 


38.5 


99-7 


15.09 
16.4s 
18.32 


16.62 ± 0.87 


Oats C 


I 
2 
3 


181. 5 


39- I 


loi .6 


22.50 
20.03 

19-33 


20.62 ± 0.74 


Buckwheat A 


I 
2 
3 


181. 5 


21.3 


100 


17.47 
13.46 
15.53 


15.49 ±0.80 


Buckwheat B 


I 
2 
3 


181. 5 


36.2 


170 


34.17 
32.60 
28.35 


31.71 ± 1.33 


Buckwheat C 


I 
2 
3 


181. 5 


45-3 


213 


34.56 
31.03 
28.09 


31.23 ± 1.32 



* No checks were used with the 1916 series; hence the results will have to be interpreted in the light 
of this fact. 



i6o 



Bulletin 406 



TABLE 2. Series 1916.* Effect of Maturity of Green Manure on Amount 
OF Nitrates Formed at the End of Twelve Months 







Num- 
ber -of 
pot 


Green 

manure 
(grams) 


Dry 
matter 
added 
(grams) 


Propor- 
tionate 
amounts 
of dry 
matter 
added 
(percent/ 


Nitrates formed in 12 
months 


Crop 


Total 
(parts per 
million) 


Average 
(parts per 
million) 


Rye 


A 

D 

C 


I 
2 
3 


181. 5 


30.9 


100 


248 
260 
252 


253 ±2.58 


Rye 


I 
2 
3 


181. 5 


40.0 


129 


97.5 
108 
108 


104 ±2.58 


Rye 


I 
2 
3 


181. 5 


530 


171. 5 


42 
42 
42 


42 ±0.00 


Oats 


A 

B 

C 


I 
2 
3 


181. 5 


38.6 


100 


270 
290 
280 


280 ± 398 


Oats 


I 
2 
3 


181. 5 


38.5 


99.7 


120 
108 
98 


109 ± 4-58 


Oats 


I 
2 
3 


181. s 


391 


loi .6 


22 

20 
19 


20 ± 0.59 


Buckwheat 


A 

B 

C 


I 
2 

3 


181. s 


21.3 


100 


136 
133 

129 


133 ± 1-39 


Buckwheat 


I 
2 
3 


181. s 


36.2 


170 


295 
279 
300 


291 ± 4-92 


Buckwheat 


I 
2 

3 


181. s 


45-3 


213 


243 
238 
230 


237 ±2.78 



* No checks were used in the 1916 series. 



Decomposition of Green Manures 



i6i 



TABLE 3. Series 1916.* Effect of Maturity of Green Manure Incubated 
IN Soil for Twelve Months on Growth of a Subsequent Wheat Crop 



Crop 


Num- 
ber of 
pot 


Green 
manure 
(grams) 


Dry 

matter 
added 
(grams) 


Propor- 
tionate 
amounts 

of dry 
matter 

added 
(per 

cent) 


Crop to 

each 
unit of 

dry 
matter 
added 
(grams) 


Straw 

crop 

(grams) 


Grain 

crop 

(grams) 


Total 

crop 

(grams) 


Average crop 
(grams) 


Rye A 


I 
3 


181. s 


30.9 


100 


1. 14 


23 40 
21 .40 
28.90 


II . 10 
10.15 
II . 20 


34-50 
31SS 
40.10 


35.38 ± 1.87 


Rye B 


I 
2 
3 


181. s 


40.0 


129 


O.S43 


12.30 
18.50 
17.70 


4.80 
4 SO 
7.40 


17.10 
23 00 
25. 10 


21.73 ±1.84 


Rye C 


I 
2 
3 


181. s 


53 


171. 5 


0.16 


5.0s 
5. 60 

7.80 


2.15 
0.80 
3-60 


7.20 
6.40 
II .40 


8.33 ±1.19 


Oats A 


I 

2 
3 


181. s 


38.6 


100 


0.847 


22.97 
23.40 
23.80 


6.53 
II . 10 
10.30 


29 SO 
34-50 
34-10 


32.70 ± 1.27 


Oats B 


I 
2 
3 


181. s 


38. S 


99.7 


0.29 


8.30 
7.00 
8.70 


4.20 
I. SO 
3 SO 


12.50 

8.50 

12. 20 


11.07 ± I 02 


Oats C 


I 
2 
3 


181. s 


39.1 


101.6 


0.20 


7.19 
4.80 
S-<3o 


0.91 
2.40 
2.60 


8.10 
7.20 
8.20 


7.83 ± 0.2s 



* No checks were used in the 1916 series. 



l62 



Bulletin 406 



TABLE 4. Series 191 7. Effect of Maturity of Green Manure on Percentage 
OF Dry Matter Humified at the End of Four Months 





Num- 
ber of 
pot 


Green 
manure 
(grams) 


Dry 
matter 
added 
(grams) 


Propor- 
tionate 
amounts 
of green 
manure 
(per cent) 


Humus 
recovered 


Humus 
due to 
treat- 
ment* 
(grams) 


Dry matter 
humified 


Crop 


from each 

pot 

(grams) 


Total 
(per cent) 


Average 
(per cent) 


Rye A 


I 
2 
3 


181. s 


56. 3 


100 


44.70 
46. 20 
43.00 


40.46 
41.96 
38.76 


74 
71 


72 ± 0.60 


Rye B 


I 
3 


180.0 


56.3 


99.1 


41 -50 
38.00 
40.10 


37.26 
33 76 
35.86 


66 
60 
64 


63 ± 1.39 


Rye C 


I 
3 
3 


150.0 


S6.3 


83 


36 
37 
33 


50 
42 
10 


32. 26 
33.18 
28.86 


57 
59 
52 


56 ± 1.59 


Oats A 


I 
2 
3 


181. 5 


52.7 


100 


49 
51 
46 


42 
S8 
96 


45.18 
47.34 
42.72 


85 
88 
80 


84 ± 1 . 79 


Oats B 


I 
2 

3 


181. 5 


52.7 


100 


33 
33 

35 


92 

50 

44 


29.68 
29.26 
31.20 


56 
55 
59 


57 ±0.99 


Oats C 


I 
2 
3 


1550 


52.7 


85.3 


33 
33 

34 


54 
14 
26 


29.30 
28. 90 
30.02 


55 
54 
56 


55 ±0.59 


Buckwheat.. .A 


I 
2 

3 


181. s 


36.5 


100 


13 
II 
IS 


77 
77 
32 


9. S3 

7 . 53 

11.08 


26 
21 
30 


26 ±1.79 


Buckwheat. . . B 


I 
2 
3 


181. s 


36.5 


100 


26 
35 
33 


39 

71 
91 


22. 15 
31.47 
29.67 


60 
86 
81 


76 ±6.17 


Buckwheat... C 


I 
2 
3 


144.0 


36.5 


79.3 


27 
29 
36 


64 
14 
34 


23.40 
24 90 
32. 10 


64 
68 
87 


73 ± 5.67 



* Untreated checks showed an average humus content of 4.24 grams to each pot. 



Decomposition of Green Manures 



163 



TABLE 5. Series 191 7. Effect of Maturity of Green Manure on Nitrification 
Process at the End of Four Months 





Num- 
ber of 
pot 


Green 
manure 
(grams) 


Dry 
matter 
added 
(grams) 


Propor- 
tionate 
amounts 
of green 
manure 
(per 
cent) 


Ni- 
trates 
in soil 
(parts 
per 
million) 


Ni- 
trates 
due to 
treat- 
ment* 
(parts 
per 
million) 


Ni- 
trogen 
added 
for each 

100 
grams 
of soil 
(milli- 
grams) 


Nitrogen in manure 
nitrified 


Crop 


Total 
(per 
cent) 


Average 
(per cent) 


Rye A 


I 
2 
3 


181. s 


56.3 


100 


172 
181 
187 


87 

96 

102 


43-3 


45 
4.9 

5.2 


4-9 ± 0.13 


Rye B 


I 
2 
3 


180.0 


56.3 


99.1 


62 
69 
60 




23 5 










Rye C 


I 
3 


150.0 


S6.3 


83 


40 
37 
37 




■■18:3 










Oats A 


I 
2 
3 


181. 5 


52.7 


100 


262 
258 
267 


177 
173 
182 


22. 7 


17.0 
16.7 
17-3 


17.0 ± 0.14 


Oats B 


I 
2 
3 


181. 5 


52.7 


100 


62 
6S 
69 




17.0 










Oats C 


I 
2 
3 


iSS-o 


52.7 


85.3 


51 
47 
44 




12.2 










Buckwheat. .A 


I 
2 

3 


181. s 


36.5 


100 


248 
238 
234 


163 
153 
149 


27.9 


12.7 
12. 1 
II. 5 


12. I ± 0.23 


Buckwheat.. B 


I 
2 
3 


181. 5 


36.5 


100 


297 
30s 

298 


212 
220 
213 


24.0 


19.0 

21 .0 

19. 1 


19-7 ± o.si 


Buckwheat.. C 


I 
2 
3 


1440 


36. 5 


79-3 


123 
129 
126 


38 
44 
41 


9.0 


9.8 
10. 2 
10. 


10. d= 0.08 



* Untreated checks showed an average nitrate content of 85 parts per million. 



164 



Bulletin 406 








cs 




fc^ 




M 




(N) 




l-l 









CM 




t^ 


a 




00 


00 


00 


t^ 


r^ 





t^ 


^ 


p +j 


J 


6 


d 


d 


CM 


d 


CM 


w 


d 


erage c 
due to 
reatmei 
(grams 


41 


4^ 


-1^ 


-H 


-« 


. 4i 


M 


4^ 


4^ 


r) 


10 


10 


t^ 


CM 


liO 


rO 


t^ 





\o 


CM 


00 


10 


OS 


ON 


CM 





NO 


> +3 


ro 


r^ 


4 


10 


(N 


VO 


m 


(N 


00 


< 


H^ 






ri 









HH 






« 10 


>r> 


10 


000 


in 


10 


000 


000 


000 


-H 1 * tn 


rO CM rO 


OMO rO 


00 t^ 


rOOO vO 


'^t^vO 


Osoo 1-H 


CM CO CM 


't-'l-n- 


COOO 1^ 


Tota 
crop 
due t 
treat 
ment 
(gram 




















>-< M r^ 


lOvO (^ 


CM vO 10 


ID CO t^ 


ONOO 


t^ t^ 10 


d dsvd 


ONO d 


00 ONt^ 


)-« t-H 11 






CM C^l CM 


hH hH 




<N CM CM 


h-l l-l 






















^ 


I- "O 


>o 


"0 


000 


mo 


10 


000 


000 


000 


Total 

crop 

grams 


\0 lOvO 


(N 00 VO 


" rOO 


" ON 


r^O ON 


CM 1-1 •+ 


irjso "0 


r^ t^ t^ 


so " 


rO 'i-a> 


00 00 " 


1000 00 


r-^ ON 


CM 


d d t^ 


CN) W 00 


1-1 00 CM 


ri 




" 




CM CM CM 


1-1 CM M 


l-l l-H 


CM CO CM 


l-H H- 1 1— 1 


HH W W 


^^ 






















'd- 10 vo 


1-H OS « 


(N 1-1 •+ 


\0 1-1 l^ 


1-1 CM rO 




OS 10 " 


r^so 


H W ^ 


.Sac 

nj 5 
t- 1- fs 


Tf TJ-UO 


4ro4 


co44 


t^l^OO 


TJ-lO CO 


CM CO CO 


CO -1- -i- 


csi ro CO 


C) CO CM 




















"^ 








































^ 


1-1 "0 


m 


too 


000 


100 


10 


000 


000 


000 


traw 

rop 

rams 


CM 


hH OS "O 


ON 0) \0 


<N 


SO 00 vO 


1-1 t^ to 


so l-l ■+ 


-1 t^ 


100 vo 


chd ■+ 


44r^ 


" ^co 


d om-i' 


00 so t^ 


00 VO ^ 


00 t^ -Tl- 


On m On 


00 On r^ 








CM " CM 


h- 1 




1-1 CM CM 


hH 




O} to 








































rop 
each 
it of 

•ry 

Ltter 
ams) 


Tl- 


CO 


OS 


00 


10 


-1- 





-1- 


n- 


C^l 







Tl- 


CM 


t-H 


J^ 


cO 


<N 


d 


6 


d 


d 


d 


d 


d 


d 


d 


^^reU 




















Propor- 
tionate 

amounts 
of green 
manure 

(per cent) 





OS 


CO 








CO 
10 








CO 

ds 





On 


00 








00 








t^ 
















l-H 






CO 


CO 


CO 


t^ 


i^ 


t^ 


m 


ID 


in 


■o 


\d 


\d 


M 


CM 


Cl 


^ 


SO 


so 


ID 


10 


10 


10 


10 


10 


CO 


CO 


rO 




















G "S^ 




















OJ ^ 


tr> 








in 


10 





•o 


10 





C ti 2 




















(U ;3 P 
S C rt 


1-4 


d 


d 


h- 1 


i-< 


10 


h-< 


HH 


ri- 


00 


00 


"0 


00 


00 


10 


CO 


00 


■+ 


^ B-3S- 
















M 






















t^n 


" CI rO 


" CM CO 


-i CM CO 


1-1 n ro 


1-1 Cs) rn 


1-1 CM CO 


l-l CM (O 


1-1 CM CO 


« n rO 




<' 




f5 




U 




< 




a 




C 




< 




p: 




L 




a 













































































I-' 

































































J! 


4J 






<u 


(U 


oi 


U3 




m 













K*^t 


>i 


>. 


rt 


cU 


% 


:3 


3 


3 




&: 




p: 




Pi 




c 




c 




C 




« 




m 




m 


1 



Decomposition of Green Manures 



i6s 



TABLE 7. Series 1918. Effect of Maturity of Green Manure on Percentage 

OF Dry Matter Humified at the End of Five Months 

The green material at each stage came from equal soil areas 





Num- 
ber of 
pot 


Green 

manure 
(grams) 


Dry 

matter 
added 
(grams) 


Propor- 
tionate 
amounts 

of dry 
matter 

added 
(per 

cent) 


Humus 
recovered 

from 
each pot 

(grams) 


Humus 
due to 
treat- 
ment* 
(grams) 


Dry matter humified 


Crop 


Total 
(per cent) 


Average 
(per cent) 


Rye A 


I 
2 
3 


181. 5 


36.3 


100 


II . 16 
14-58 
11.14 


4-43 
7.8s 
4.41 


12.2 
21.6 
12. 1 


iS-3 ± 2.39 


Rye B 


I 
2 
3 


3^3-0 


78.0 


215 


12.44 
13 07 
14.12 


5-71 
6.34 
7.39 


7.3 
8.1 
95 


8.3 ± 0.47 


Rye C 


I 

2 

3 


366.0 


150.0 


413 


16.72 
19.90 
20.02 


9-99 
13 17 
13-29 


6.6 

8.8 
8.8 


8.1 ± o.si 


Oats A 


I 
2 
3 


181 4 


34-4 


100 


13 93 
13-81 
13 12 


7.20 
7.08 
6.39 


21 .0 
20.0 
igo 


20.0 ± o..;o 


Oats B 


I 
2 
3 


2730 


6j.o 


183 


iS-69 
17-39 
17.36 


8.96 
10 66 
10.63 


14.1 
16.9 
16.8 


15.9 ± 0.53 


Oats C 


I 
3 


350.0 


122.0 


355 


23-97 
23-38 
24.03 


17.24 
16.6s 
17-30 


14. 1 
13-9 
14. 1 


14.0 ±0.04 


Buckwheat.. .A 


I 
3 


181. 5 


27.2 


100 


17.00 
14.93 
14-63 


10.27 
8.20 
7.90 


38.0 
30.0 
29.1 


32.4 ± 2.2s 


Buckwheat... B 


I 

2 

3 


34S-0 


69.0 


254 


19-82 
19-52 
21.62 


13 09 
12.79 
14.89 


18.9 
18.5 
21.6 


19.7 ± 1.31 


Buckwneat...C 


I 
2 
3 


400.0 


100. 


368 


21.03 
24-33 
22. 16 


14.30 
17-60 
15-43 


14-3 
17.6 

IS. 4 


15.8 ±0.73 



* Untreated checks showed an average humus content of 6 . 73 grams to each pot. 



1 66 



Bulletin 406 



TABLE 8. Series 1918. Effect of Maturity of Green Manure on Nitrification 

Process at the End of Five Months 

The green material at each stage came from equal soil areas 





Num- 
ber of 
pot 


Green 
manure 
(grams) 


Dry 

matter 
added 
(grams) 


Propor- 
tionate 
amounts 

of dry 
matter 

added 
(per 

cent) 


Ni- 
trates 
in soil 
(parts 

per 
million) 


Ni- 
trates 
due to 
treat- 
ment* 
(parts 
per 
million) 


Ni- 
trogen 
added 
for each 

100 
grams 
of soil 
(milli- 
grams) 


Nitrogen in manure 
nitrified 


Crop 


Total 
(per 
cent) 


Average 

(per cent) 


Rye A 


I 
2 
3 


181. 5 


36.3 


100 


190 
190 
175 


142 
142 

127 


24.0 


12.56 
12.56 
12. 20 


12.44 ±0.10 


Rye B 


I 
2 

3 


3230 


78.0 


215 


i6s 
160 
160 


117 
112 
112 


33-5 


7.40 
7-30 
7-30 


7-30 ±0.02 


Rye C 


I 
2 
3 


366.0 


150.0 


413 


44 

52 

54 




4 
6 


' '66!o 


0.00 
0.06 
0.06 


- 04 ± . 007 


Oats A 


I 
2 
3 


181. 4 


34.4 


100 


280 
267 

272 


232 
219 

224 


' '26!o 


15-80 
15.40 
IS. 70 


15 63 ± 0.08 


Oats B 


I 

2 

3 


273 


63.0 


183 


195 
165 
180 


147 
117 
132 


"28;8 


9.45 
9. 10 
9-35 


9 30 ±0.08 


Oats C 


I 
2 
3 


350.0 


122.0 


355 


ISO 
158 
142 


102 

no 

94 


37.0 


6.23 
6.35 
6.05 


6.21 ± - 06 


Buckwheat. .A 


I 
2 
3 


181. 5 


27.2 


100 


400 
385 

415 


352 
337 
367 


22.4 


35-30 
34-00 
36.80 


35.37 ±0.17 


Buckwheat.. B 


I 
2 
3 


34SO 


69.0 


254 


533 
533 
571 


485 
485 
523 


52.0 


20.00 
20.00 

22.40 


20.80 ±0.64 


Buckwheat. . C 


I 
2 
3 


400.0 


100. 


368 


460 

440 
492 


412 
392 
444 


"56 .5 


18.00 
17.00 
19.60 


18.20 ±0.55 



* Untreated checks showed an average nitrate content of 48 parts per million. 



Decomposition of Green Manures 



167 



Average crop 

due to 

treatment 

(grams) 


CO 


On 

d 


dv 


10 

d 

4^ 



dv 


d 

10 

00 





00 
4- 


On 

d 
d 


00 

d 


On 

d 
41 

On 
C) 


Total 
crop 
due to 
treat- 
ment* 
(grams) 


0) t^ CN 
C^l CS (N 


r^ c) r^ 


t^ t^ t^ 

00 \0 rt 


00 00 d 

« « M 


I^ t^ (N 

00 vd d 


OMOw 


ro 10 r^ 

00 OS N 
1-1 1-1 P» 


10 w r^ 


N 00 r^ 
10 p< 


Total 

crop 

(grams) 


l-H ID 


100 

00 10 0^ 


000 


>0«0 

(N 0) (M 


10 

HH HH I— 1 


M 00 Tf 

d dvd 


VO 00 
M (S 01 


rJ-00 
On "0 r^ 

HH l-( HH 


ID 1-1 
On t^ U-> 


Grain 
crop 

(grams) 


(Mr)" 


d « i-i 


00 o\ 

i-H <N w 


10 ON 
(N (N w 


\0 >000 

1— 1 HH hH 


0) i^ 


fO -i-O 
<N (N fO 


00 ON >-i 

)-H HH HH 


rO <N 00 


Straw 

crop 

(grams) 


^3 \0 
0) 0) (S 


H- row 


M M 
l-H CMO 


10 liO^ 

n 

(S (N 0) 


■^ 10 t^ 

— ON ri 


« ^ 

ON OMO 


d i-i -+ 
0) IN 0) 


NO 0^ ON 

r^ ro 10 


M On 0) 

00 10 ro 


Crop 
to each 
unit of 

dry 
matter 
(grams) 


vD 

d 


d 


d 


d 


d 


d 


d 


On 

d 


d 


Propor- 
tionate 
amounts 
of dry 
matter 
added 
(per cent) 


8 

>-* 


10 









00 


10 

ID 

fO 








00 

NO 


Dry 

matter 
added 
(grams) 






00 




d 
10 


4 






0) 






NO 




d 




Green 
manure 
(grams) 


10 

00 



fo 





00 



fO 




d 
10 


10 

00 






d 




" CM ro 


1-1 rj rO 


i-i n rD 


1-1 M ro 


« 0) CO 


1-1 tN re 


h-c p< ro 


M <N) fO 


►I M ro 


6 


< 

> 


~ 


> 

Pi 




> 


% 












w 

0] 




1 


•4-3 

pq 




p: 
a 




1 

pq 





i68 Bulletin 406 

TABLE 10. Comparison of the Amounts of Dry Matter Humified from Crops 
Incorporated with Soil at Different Stages of Growth* 
(The first letter appearing on the left side of the column represents the greater 
percentage of humification. For the differences to be significant, they must be 3.8 
times the probable error.) 



Crop 


Series 191 7 
(Data given in table 4) 


Series igi'S 
(Data given in table 7) 


Stages of 

growth 

compared 


Difference 
(per cent) 


Stages of 

growth 

compared 


Difference 
(per cent) 


Rye • 


A and B 
A and C 
B and C 


9 ± I-5I 
16 ± 1.67 

7 ± I • 95 


A and B 
AandC 
B and C 


7-0 ±2.43 
7 . 2 ± 2 . 44 
. 1 ± . 69 


Oats 1 


A and B 
A and C 
B and C 


27 ±2.04 

29 ± 1.87 

2 ± 1. 14 


A and B 
A and C 
B and C 


5.0 ± 0.90 
6.0 ± 0. 40 
1.0 ± 0.80 


Buckwheat ■ 


B and A 
B and C 
Cand A 


50 ±6.45 

3 ±8.41 

47 ±5-93 


A and B 
B and C 
A and C 


12.7 ± 2.13 

3-9 ± 1-49 
16.6 ± 1.84 



* No checks were used in the 1916 series; hence for that series no calculations could be made. 



TABLE II. Comparison of the Amounts of Nitrogen Nitrified in Crops 
Incorporated with Soil at Different Stages of Growth* 
(The first letter appearing on the left side of the column represents the greater 
percentage of nitrification. For the differences to be significant, they must be 3.8 
times the probable error.) 





Series 191 7 
(Data given in table 5) 


Series 19 18 
(Data given in table 8) 


Crop 


Stages of 

growth 

compared 


Difference 
(per cent) 


Stages of 

growth 

compared 


Difference 
(per cent) 


r 






A and B 
AandC 
BandC 


5. II ± 0. 10 


Rye ] 




12.40 ± 0. 10 




7.29 ± 0.02 








r 






A and B 
A and C 
B and C 


6.33 ± 0. II 


Oats ] 




9.42 ± 0. 10 






3.09 ± 0. 10 








Buckwheat ■ 


B and A 
B and C 
A and C 


7-6 ± .55 

9-7 ± 51 

2.1 ± .24 


A and B 
A and C 
B and C 


14.57 ±0.65 

17.17 ±0.57 

2 . 60 ± 0. 84 



* No checks were used in the 1916 series; hence for that series no calculations could be made. 



^ 



LiBRftRY OF CONGRESS 



000 937 583 1 



